As described in a previous patent application by this applicant, EP2806553 (whose disclosure corresponds to that of related applications US2014/0347104 and CN104184309), numerous methods of performing mass spectrometry rely on the application of high frequency voltage waveforms to components of a mass spectrometer. For example, ion optical devices such as ion guides, ion traps, mass filters and other devices may all require such voltage waveforms, as is well described in the literature.
The previous patent application by this applicant, EP2806553, further described that direct switching methods provide a significant advantage over resonant circuits in that the frequency of the voltage waveform can be easily changed during operation. However, “hard switching” techniques (described in more detail below), tend to be inefficient and power consumption is relatively large.
In view of these considerations, EP2806553 proposed various circuits for generating a voltage waveform at an output node in which a control unit was configured to change a voltage at the output node by controlling a voltage rail switch and a bidirectional switch so that, if a load capacitance is connected to the output node, a resonant circuit is established between the inductor and the load capacitance. The circuits proposed by EP2806553 were referred to as “energy recovery” circuits, as they helped the voltage waveform to be generated in a more energy efficient manner.
However, whilst the circuits proposed by EP2806553 provide a significant improvement in energy efficiency compared with “hard switching” techniques in which resonant circuits are not used (e.g. as disclosed in WO01/29875), the present inventors have found that the “energy recovery” circuits proposed in EP2806553 still result in a significant amount of current to be drawn from high voltage power supplies typically used in generating the voltage waveform, which can cause a lack of stability in the voltages provided by the high voltage power supplies (which may be highly problematic in certain applications, such as mass spectrometry). As such, the present inventors believe it would be desirable to further improve such circuits.
The present invention has been devised in light of the above considerations.